For many applications, it is desirable to have multiple signals simultaneously use the same channel. Such an approach conserves bandwidth, simplifies modulation and demodulation parameters, reduces cost, etc. Time-sharing a single channel requires careful coordination of operation of transmitting and receiving stations, possible need for a separate timing signal (which may be particularly disadvantageous in a wireless or atmospheric communication system) and furthermore reduces the amount of data or information that can be transmitted in a given time.
For example, a communication system can be provided in which several receiving stations are located at various points and receive data from a single transmitting station which is located at another point. For such a system, control signals could be transmitted continuously to all receivers, while each set of data signals would be transmitted only between a pair of platforms. For such a system, it is obviously desirable that all such signals occupy the same frequency band and be simultaneously transmitted, so that for example control is not lost while data is being transmitted. The present invention fulfills these needs.
If separate bands are used, then separate modulators, spreaders (if used), upconversion to RF transmission frequency, transmitters, power amplification for each transmission and additional power supplies would be necessary. Likewise, at the receiving end, in order to receive more than one transmission at the node or site at the same time, additional demodulators, downconverters, power supplies, etc. must also be provided, or else not receiving both signals simultaneously must be conceded. Frequency allocations also become unwieldy. Either situation would be cluttered and chaotic.